The invention relates to providing a part comprising a substrate in which at least a portion adjacent to a surface is made of a refractory material containing silicon, with protection while the part is being used at high temperature in an oxidizing medium, the protection being obtained by forming an environmental barrier on the surface of the substrate.
The invention relates in particular to protecting parts made of refractory composite material such as a ceramic matrix composite (CMC) material containing silicon, in particular a CMC having fiber reinforcement made of ceramic fibers, e.g. silicon carbide (SiC) fibers or fibers based on SiC, and a matrix made at least in part out of SiC.
A particular field of application of the invention is that of protecting CMC parts that form hot portions of gas turbines, such as combustion chamber walls, or turbine rings, or turbine nozzles, or turbine blades, for aeroengines and for industrial turbines.
Document WO 2010/072978 describes forming an environmental barrier having at least one self-healing layer based on a system of oxides formed by at least one rare earth oxide, silica, and alumina. The composition of the self-healing layer is selected so as to conserve a majority solid phase up to at least about 1400° C., while presenting at least one liquid phase at a temperature equal to or higher than about 1400° C., the liquid phase being in sufficient quantity to perform a self-healing function at such a temperature.
Nevertheless, there exists a need to protect CMC parts that are exposed in service to temperatures lying in a range of temperatures below 1400° C. This applies in particular when the fiber reinforcement of the CMC material is made of SiC fibers or of SiC-based fibers having properties that become clearly degraded at 1400° C., but of cost that is significantly less than that of SiC fibers capable of withstanding a temperature of 1400° C. or more without damage.